The Preclinical Animal Core is the primary vehicle by which breast cancer investigators generate pre-clinical data in vivo and mechanistically validate hypotheses generated in vitro. Pre-clinical animal tumor model systems are essential to evaluate the anti-tumor efficacy, pharmacokinetics and biodistribution of innovative anti-rumor agents. The Preclinical Animal Core assists in experimental design involving animals, performs technical aspects of pre-clinical testing in vivo, maintains a well-characterized repository of breast cancer cell lines and primary tumors optimized for passage in animals, develops and incorporates new tools and resources for preclinical testing, and fosters inter-SPORE collaborations involving in vivo tumor models. The availability of centralized cell and animal resources, and personnel with expertise in tumor cell propagation in vitro and in vivo, drug delivery and measurement endpoints, ensures appropriate experimental design and data reproducibility, compliance with local and federal regulatory guidelines for tumor-bearing animals, and maximum resource utilization through coordinated animal purchasing and housing. Human tumor xenografts implanted into the mammary fat pads of immune-deficient mice (nu/nu) are the primary pre-clinical model used by most SPORE investigators. Cell xenografts are selected based upon the genomic and phenotypic features desired for hypothesis testing and agent evaluation. The Core also develops and explores new assays and resources to enhance the ability of SPORE investigators to quantify induce-perturbations at multiple levels such as proliferation, invasion and metastases. The main services/resources provided by the Preclinical Animal Core are to: 1. Design and conduct preclinical studies using xenografts to support the development and translation of innovative anticancer therapies. 2. Enhance investigator capabilities to investigate the anti-proliferative effects of novel agents on early tumors and disseminated disease by optimizing assays to quantify tumor dissemination using species-specific DNA probes and in vivo tumor cell imaging with bioluminescent reporters. 3. Consult and assist SPORE investigators on potential uses ofxenograft and other animal models of human breast cancer and promote inter-SPORE collaborations with investigators using pre-clinical animal tumor models.